COMPLEXES OF CUCURBITURIL WITH ALKYL MONOAMMONIUM AND DIAMMONIUM IONSIN AQUEOUS FORMIC-ACID STUDIED BY CALORIMETRIC TITRATIONS

The thermodynamic data of the complexation reaction between the ligand cucurbituril and different alkylmonoamine and alkyldiamine hydrochlor ides have been studied in aqueous formic acid. The stability constants , the reaction enthalpies and the reaction entropies are obtained from calorimetric titrations. At both rims of the cavity of cucurbituril t he carbonyl groups interact with ions by ion-dipole interactions. If a mmonium ions with longer alkyl chains enter the hydrophobic cavity of cucurbituril hydrophobic interactions participate in the complex forma tion. The hydrophobic contribution to the reaction enthalpy is calcula ted for the alkyl monoammonium ions. In 50% (v/v) formic acid the enth alpies of the hydrophobic interactions contribute more to the experime ntal reaction enthalpy than the ion-dipole interactions. (C) 1997 Else vier Science B.V.